Genotypic studies have shown that enteroinvasive Escherichia coli (EIEC) and Shigella form a single pathotype sharing a common composition of carbohydrates in the lipopolysaccharide (LPS).In this study 23 E. coli strains isolated from different sources, were characterized. Serotyping was performed with 187 O and 53 H E. coli and 46Shigella sera samples. PCR assays to lacY, lacZ, uidA,cyd, ipaH, wzx,wzy,ltA,stp, cfaI,sc3 and phylogenetic groups were performed. A serum against the E. coli 44037 strain was obtained. Serotyping of 23 strains only showed reaction against S. boydii 18 and 44037antisera and were positive for lacY, lacZ, uidA and cyd, but negative for ipaH. The same gene analysis ofS. boydii 18 strain showed positive reaction for ipaH, uid andcyd but negative for lacZ and lacY. Both E. coli and S. boydii 18 strains amplified wzx and wzy genes. The genes ltA,stp, cfaI and sc3 were detected in 14 (61%), 6 (26%), 21 (91%) and 13 (57%) of E. coli strains. The phylogenetic analysis included the E. coli strains in: clade I (35%), and A (22%), B1 (22%), B2 (13%) and D (4 %) groups. The 23 E. coli strains isolated from children with diarrhea and dairy cattle reacted against S. boydii 18 but that amplified ETEC genes, constitute a new serogroup (44037) with the serotypes 44037:NM, H2 and H16 in children and 44037:H3, H9 and H48 from dairy cattle.Copy Right, IJAR, 2016,. All rights reserved. …………………………………………………………………………………………………….... Introduction:-Diarrheal diseases are an important public health problem around the world with more than 2 million related deaths being reported each year with children under 5 years of age in developing countries being particularly affected (Kosek, 2003). Escherichia coli is one of the most common etiological agents responsible for childhood diarrhea and is one of the most important public health problems in developing countries (Davidson, 2002). The traditional Shigella genus consists of four species: S. dysenteriae; S. flexneri,S. boydii and S. sonnei, or Shigellasubgroups A, B, C and D(Ewing, 1986). However, recent genotyping studies have shown that the four INTERNATIONAL JOURNAL OF ADVANCED RESEARCH (IJAR)Corresponding Author:-Armando Navarro Address:-Department of Public Health, Faculty of Medicine, Universidad Nacional Autónoma de México ISSN: 2320-5407 Int. J. Adv. Res. 4(10), 629-638 630 species are closely related to enteroinvasive E. coli (EIEC), which suggests that distinct ancestral lineages of E. coli gave rise to EIEC and Shigella through a process of convergent evolution by acquiring of similar pathogenic characteristics (Pupo, 2000;Peng, 2006;Yang, 2007;Peng, 2009). According to a study based on analyzing housekeeping genes, both genera constitute one single pathotype of E. coli (Lan, 2004).The identification of somatic (O) surface antigens and flagellar (H) antigens using specific antibodies has been used for many years to characterize enterobacteria antigenically (Orskov, 1984). Shigella and E. coli present a wide diversity in terms of the combination of O and...